Relaxationsoftening

Relaxationsoftening is a term used in materials science and engineering to describe a coupled phenomenon in which a material exhibits stress relaxation under a fixed strain while also losing stiffness or strength as damage evolves. The concept combines two well-known effects: viscoelastic relaxation, where internal rearrangements reduce stress over time under constant strain, and softening, a degradation of material properties such as modulus or yield strength due to microstructural damage, aging, or thermal effects.

Mechanisms often involve both time-dependent viscoelastic processes and damage that progresses with deformation. Relaxation reduces the stored stress, while softening reflects a weakening of the material’s response, potentially accelerating further relaxation as cracks, voids, or phase changes accumulate. In many polymers and composites, the interaction between relaxation and damage can lead to nonlinear, rate- and temperature-dependent behavior.

Modeling approaches couple viscoelasticity with damage mechanics. A common framework expresses stress as sigma = (1 − D) C : ε for small strains, with D ∈ [0,1] a damage variable and time dependence introduced via a relaxation modulus G(t) or a Prony-series representation. The damage evolution law Ḋ = g(ε, σ, T) describes how softening progresses with strain energy or loading history.

Measurement and applications: Relaxationsoftening can be observed in creep-relaxation tests, stress-relaxation under ramp loading, and dynamic mechanical analysis. It is relevant for polymers, asphalt, concrete, and some metals at elevated temperatures, as well as geotechnical materials like soils and rocks. See also creep, stress relaxation, damage mechanics, softening, viscoelasticity.